Non-aromatic compound removal systems for para-xylene production

ABSTRACT

Selective removal of non-aromatic hydrocarbons from a xylene isomerization process for para-xylene production is accomplished using a membrane unit positioned within a xylene recovery loop. The membrane unit may include a one-stage or multi-stage (e.g., two-stage) membrane system and may be configured to separate a membrane unit product stream from a non-aromatics rich stream, which can be removed from the xylene recovery loop. The membrane unit may have a xylene permeance of about 60 gm/m2/hr/psi and a xylene to non-aromatic permeance ratio of about 15.

FIELD OF THE INVENTION

The present disclosure is directed to non-aromatic compound removalsystems and, more particularly, to systems and methods for removingnon-aromatic compounds from a xylene isomerization process forpara-xylene production.

BACKGROUND

Of the xylene isomers, para-xylene is by far the most important forcommercial applications, particularly as a feedstock for production ofmany industrial chemicals. Current xylene isomerization processes aim toproduce and separate the para-xylene isomer from the meta- andortho-xylene isomers using a variety of methods. Typically, theseprocesses involve the use of a feed stock, for example a reformate, thatincludes mixed xylenes and non-aromatic compounds (or non-aromatics).

After separation of para-xylene, the unconverted meta- and ortho-xylenesare recycled back to the isomerization reactor, along with thenon-aromatic compounds. The concentration of non-aromatics continues toincrease within the recycle loop as fresh feed containing non-aromaticscontinues to be added to the isomerization reactor feed and para-xylenecontinues to be removed from the recycle loop. Due to this, non-aromaticconcentration continues to build in the recycle loop negativelyaffecting the para-xylene yield, and overall process efficiency andcapacity.

In current commercial practice, this increase in concentration ofnon-aromatic compounds is controlled by purging a certain amount of therecycle stream, which results in the loss of xylenes along with thenon-aromatics. In some instances, where a continuous purge isinsufficient to control non-aromatic compound build-up, the entirerecycle inventory is periodically dumped.

Accordingly, there is need for improved systems for selectively removingnon-aromatic compounds from a xylene isomerization process forpara-xylene production to improve yield, and overall process efficiency,and capacity. The disclosed systems and methods are directed toovercoming these and other considerations.

SUMMARY

In various aspects, systems and methods for removing non-aromaticcompounds from a xylene isomerization process for para-xylene productionare provided. A non-aromatic compound removal system may include one ormore components of a, a xylene recovery loop, which may include a xylenesplitter, a para-xylene recovery unit, an isomerization unit, adeheptanizer unit, and a clay treater, and a membrane unit (e.g., aone-stage or multi-stage system) strategically positioned within thexylene recovery loop depending on the application. Regardless of itsposition within the xylene recovery unit, the membrane unit may beconfigured to preferentially permeate xylenes such that it allows othermolecules (e.g., non-aromatics) to permeate more slowly than xylene ifit allows those other molecules to permeate at all. In this manner, themembrane unit separates a non-aromatics rich stream from other streamswithin the xylene recovery loop so that the non-aromatics rich streamcan be removed while the xylene recovery loop efficiently andeffectively (e.g., at a higher yield and/or capacity level forxylene-containing streams, which can occupy the space of the removednon-aromatics) processes the remaining streams and/or new reformatestream(s). By removing the non-aromatics rich stream, the xylenerecovery loop can operate at a higher yield, more efficiently andeffectively, with a higher capacity for xylene-containing streams, andlower cost. It can also operate continuously without requiring stoppageof the xylene isomerization process to dump contents of the xylenerecovery loop in an effort to purge the non-aromatics. The membrane unitmay be configured to present a xylene permeance of between 5-150gm/m²/hr/psi (e.g., between about 40-80 gm/m²/hr/psi in some embodimentsand about 60 gm/m²/hr/psi in other embodiments) and a xylene tonon-aromatic permeance ratio of 3-70 (e.g., between about 10-25 in someembodiments and about 15 in other embodiments). It is advantageous tomaximize both the xylene permeance and xylene to non-aromatic permeanceratio to improve performance, though doing so requires balancing the twovalues as the xylene permeance and xylene to non-aromatic permeanceratio are inversely related (e.g., increasing the value of one decreasesthe other). Increasing the xylene permeance helps to reduce the requiredsurface area for the membrane unit. Increasing the xylene tonon-aromatic permeance ratio provides cleaner separation between xylenesand non-aromatics (e.g., at a ratio of 15, xylene is permeating throughthe membrane 15 times faster than non-aromatics). The inputs, outputs,and efficiency of the membrane unit vary based on its position withinthe xylene recovery loop.

For example, in one aspect, the membrane unit may be positioned upstreamof the xylene splitter such that it is configured to receive a reformatestock stream and produce a non-aromatics rich stream and a membrane unitproduct stream. In this configuration (i.e., with the membrane unitpositioned upstream of the xylene splitter), the xylene splitter may beconfigured to receive the membrane unit product stream and produce amixed xylene stream, which may include para-xylene, ortho-xylene, andmeta-xylene. Other components (e.g., the para-xylene recovery unit,isomerization unit, deheptanizer unit, and clay treater) of the xylenerecovery loop may be configured to receive and process the mixed xylenestream, which may include processing the mixed xylene stream in thepara-xylene recovery unit to produce a para-xylene rich stream and apara-xylene lean stream, processing the para-xylene lean stream in theisomerization unit to produce an isomerization unit product stream,feeding the isomerization unit product stream into the deheptanizer unitto produce a xylene rich stream, processing the xylene rich streamthrough a clay treater to produce a clay treated stream, and feeding theclay treated stream back into the xylene splitter for recirculationwithin the xylene recovery loop.

In another exemplary aspect, the membrane unit may be repositioneddownstream of the xylene splitter and upstream of the remainingcomponents of the xylene recovery loop. In this configuration, thexylene splitter may be configured to receive a reformate stock streamand produce a mixed xylene stream, which may include para-xylene,ortho-xylene, and meta-xylene. The membrane unit may be in direct fluidcommunication with the xylene splitter such that it is configured toreceive the mixed xylene stream and produce a non-aromatics rich streamand a membrane unit product stream. The para-xylene recovery unit may bein direct fluid communication with the membrane unit such that it isconfigured to receive the membrane unit product stream and produce apara-xylene lean stream. The isomerization unit may be in direct fluidcommunication with the para-xylene recovery unit and configured toprocess the para-xylene lean stream to produce an isomerization unitproduct stream, which is in turn fed into the deheptanizer unit. Thedeheptanizer unit may be in direct fluid communication with theisomerization unit and configured to produce a xylene rich stream, whichcan then be processed through the clay treater. The clay treater may bein direct fluid communication with the deheptanizer unit and configuredto produce a clay treated stream, which can then be fed into the xylenesplitter for recirculation within the xylene recovery loop.

In a further exemplary aspect, the membrane unit may be repositioneddownstream of the xylene splitter and between the para-xylene recoveryunit and the deheptanizer unit of the xylene recovery loop. In thisconfiguration, the xylene splitter may be configured to receive areformate stock stream and produce a mixed xylene stream, which mayinclude para-xylene, ortho-xylene, and meta-xylene. The para-xylenerecovery unit may be in direct fluid communication with the xylenesplitter and configured to receive the mixed xylene stream from thexylene splitter and produce a para-xylene lean stream. The membrane unitmay be in direct fluid communication with the para-xylene recovery unitand configured to receive the para-xylene lean stream and produce anon-aromatics rich stream and a membrane unit product stream. Becausethe membrane unit may be configured to receive the para-xylene leanstream rather than a reformate stream or mixed xylene stream, it mayoperate more efficiently in this position. The deheptanizer unit may bein fluid communication with the para-xylene recovery unit (e.g., by wayof the membrane unit and, optionally, an isomerization unit) andconfigured to produce a hydrocarbon stream. Optionally, a clay treatermay be in direct fluid communication with the deheptanizer unit and thexylene splitter such that it is configured to receive the xylene richstream from the deheptanizer unit and produce a clay treated stream,which can then be fed to the xylene splitter for recirculation withinthe xylene recovery loop.

In yet another exemplary aspect, the membrane unit may be repositioneddownstream of the deheptanizer unit of the xylene recovery loop. In thisconfiguration, the xylene splitter may be configured to receive areformate stock stream and produce a mixed xylene stream, which mayinclude para-xylene, ortho-xylene, and meta-xylene. The para-xylenerecovery unit may be in direct fluid communication with the xylenesplitter and configured to receive the mixed xylene stream from thexylene splitter and produce a para-xylene lean stream. The deheptanizerunit may be in fluid communication with the para-xylene recovery unit(e.g., directly or, optionally, indirectly by way of an isomerizationunit) and configured to produce a hydrocarbon stream. The membrane unitmay be in direct fluid communication with the deheptanizer unit andconfigured to receive the hydrocarbon stream and produce a non-aromaticsrich stream and a membrane unit product stream. Optionally, a claytreater may be in direct fluid communication with the deheptanizer unitand the xylene splitter such that it is configured to receive the xylenerich stream from the deheptanizer unit and produce a clay treatedstream, which can then be fed to the xylene splitter for recirculationwithin the xylene recovery loop.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosednon-aromatic compound removal system with multiple configurations;

FIG. 2 is a flow chart illustrating a method for removing non-aromaticcompounds from a xylene isomerization process for para-xylene productionin accordance with an example embodiment, which may be used inconjunction with the system of FIG. 1 in a first configuration;

FIG. 3 is a flow chart illustrating a method for removing non-aromaticcompounds from a xylene isomerization process for para-xylene productionin accordance with an example embodiment, which may be used inconjunction with the system of FIG. 1 in a second configuration;

FIG. 4 is a flow chart illustrating a method for removing non-aromaticcompounds from a xylene isomerization process for para-xylene productionin accordance with an example embodiment, which may be used inconjunction with the system of FIG. 1 in a third configuration; and

FIG. 5 is a flow chart illustrating a method for removing non-aromaticcompounds from a xylene isomerization process for para-xylene productionin accordance with an example embodiment, which may be used inconjunction with the system of FIG. 1 in a fourth configuration.

DETAILED DESCRIPTION

Although certain embodiments of the disclosure are explained in detail,it is to be understood that other embodiments are contemplated.Accordingly, it is not intended that the disclosure is limited in itsscope to the details of construction and arrangement of components setforth in the following description or illustrated in the drawings. Thedisclosure is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the embodiments,terminology will be resorted to for the sake of clarity. It is intendedthat each term contemplates its broadest meaning as understood by thoseskilled in the art and includes all technical equivalents which operatein a similar manner to accomplish a similar purpose.

Herein, the use of terms such as “having,” “has,” “including,” or“includes” are open-ended and are intended to have the same meaning asterms such as “comprising” or “comprises” and not preclude the presenceof other structure, material, or acts. Similarly, though the use ofterms such as “can” or “may” are intended to be open-ended and toreflect that structure, material, or acts are not necessary, the failureto use such terms is not intended to reflect that structure, material,or acts are essential. To the extent that structure, material, or actsare presently considered to be essential, they are identified as such.

By “comprising” or “containing” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

Ranges can be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another embodiment includes fromthe one particular value and/or to the other particular value.

The term “aromatic” is used herein to designate a hydrocarbon-basedorganic compound containing at least one aromatic ring. The term“non-aromatic” is used herein to designate a hydrocarbon compound havingno aromatic nucleus. The term “mixed xylene” is used herein to designatea mixture comprising meta-xylene, ortho-xylene, and para-xylene.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified, nor is thedisclosure limited by the order in which the method steps are expresslyidentified. Similarly, it is also to be understood that the mention ofone or more components in a system does not preclude the presence ofadditional components or intervening components between those componentsexpressly identified, nor is the disclosure limited by the order inwhich the components are expressly identified.

The components described hereinafter as making up various elements ofthe disclosure are intended to be illustrative and not restrictive. Manysuitable components that would perform the same or similar functions asthe components described herein are intended to be embraced within thescope of the disclosure. Such other components not described herein caninclude, but are not limited to, for example, similar components thatare developed after development of the presently disclosed subjectmatter.

As described above, current xylene isomerization processes forpara-xylene production use feed stocks that contain certain amounts ofnon-aromatic compounds. These non-aromatics are recycled back to anisomerization reactor along with the unconverted ortho- and meta-xylenesafter separation of para-xylene. The concentration of non-aromaticswithin the recycle loop increases as fresh feed stock containingnon-aromatics continues to be added to the isomerization reactor feed.The continual build-up of non-aromatics in the system results indecreased recycle loop capacity for xylene-containing streams (e.g., dueto the space occupied by the non-aromatics within the recycle loop),efficiency, and para-xylene yield. Certain amounts of recycle streamsmust therefore be periodically purged or even completely dumped, leadingto the loss of xylenes along with the non-aromatics.

Disclosed herein, therefore, are systems and methods for selectivelyremoving non-aromatic compounds from a xylene isomerization process forpara-xylene production by employing a membrane unit in one or morepositions within the system. The membrane unit continually removesnon-aromatics from the process, minimizing/eliminating the need forpurging or dumping of any process stream. To accomplish this, themembrane unit may preferentially permeate xylene while either notpermeating other molecules (e.g., non-aromatics) or permeating thoseother molecules more slowly in order to separate the xylenes from theother molecules. This separation is not accomplished by filtering basedon size of the molecules, but rather by permitting xylene to dissolveand diffuse through the membrane unit preferentially over non-aromatics.

References will now be made in detail to example embodiments of thedisclosed technology, examples of which are illustrated in theaccompanying drawings and disclosed herein. Wherever convenient, thesame reference numbers will be used throughout the drawings to refer tothe same or like parts.

FIG. 1 illustrates a non-aromatic compound removal system 100 havingmultiple in-use configurations for removing non-aromatic compounds froma xylene isomerization process for para-xylene production in accordancewith some embodiments. As shown, the system 100 may include a xylenerecovery loop 101, which may include one or more components of a xylenesplitter 110, a para-xylene recovery unit 120, an isomerization unit130, a deheptanizer unit 140, and a clay treater 150, and at least oneof a membrane unit 160A, 160B, 160C, and 160D positioned as shown withinthe system 100. For example, the membrane unit 160A may be positionedupstream of the xylene splitter 110 in a first configuration of thesystem 100, the membrane unit 160B may be positioned between the xylenesplitter 110 and the para-xylene recovery unit 120 in a secondconfiguration of the system 100, the membrane unit 160C may bepositioned between the para-xylene recovery unit 120 and theisomerization unit 130 in a third configuration of the system 100, andthe membrane unit 160D may be positioned downstream of the deheptanizerunit 140 in a fourth configuration of the system 100, as described inmore detail below. In some embodiments, a single membrane unit ormultiple membrane units 160A-D may be used within the system 100. Thecomponents of the system 100 are in fluid communication with oneanother, directly or indirectly, and collectively configured to receivea reformate stream and produce a para-xylene rich stream, anon-aromatics rich stream, and a heavier hydrocarbon stream that mayinclude C9 and C10 hydrocarbons.

The xylene splitter 110 may be in direct fluid communication with one ormore of a reformate stream, the membrane unit 160A, the membrane unit160B, the para-xylene recovery unit 120, and the clay treater 150 suchthat it is configured to receive, directly or indirectly, a reformatestock stream 102 (e.g., from a source external to the system 100) or amembrane unit product stream 162A (e.g., from membrane unit 160A) and tooutput a xylene rich stream 112 and a heavier hydrocarbon stream 114that may include C9 and C10 hydrocarbons. The xylene splitter 110 mayinclude a fractional distillation column, selective sorption unit, orother technology known in the art.

Positioned downstream of the xylene splitter 110 within the xylenerecovery loop 101, the para-xylene recovery unit 120 may be in directfluid communication with one or more of the xylene splitter 110, themembrane unit 160B, the membrane unit 160C, the isomerization unit 130,and the deheptanizer unit 140 such that it is configured to receive,directly or indirectly, the mixed xylene stream 112 (e.g., from thexylene splitter 110) or a membrane unit product stream 162B (e.g., frommembrane unit 160B) and to output a para-xylene lean stream 122 and apara-xylene rich stream 124. The para-xylene recovery unit 120 mayinclude one or more of any of the para-xylene recovery units known inthe art, including, for example, a crystallization unit, an adsorptionunit (such as a PAREX™ unit or an ELUXYL™ unit), a reactive separationunit, a membrane separation unit, an extraction unit, a distillationunit, an extractive distillation unit, a fractionation unit, a simulatedmoving bed type of recovery unit, or any combination thereof.

Positioned further downstream within the xylene recovery loop 101, theisomerization unit 130 may be in direct fluid communication with one ormore of the para-xylene recovery unit 120, the membrane unit 160C, andthe deheptanizer unit 140 such that it is configured to receive,directly or indirectly, a hydrogen stream 104 (e.g., from a sourceexternal to the system 100) and the para-xylene lean stream 122 (e.g.,from the para-xylene recovery unit 120) or a membrane unit productstream 162C (e.g., from membrane unit 160C), and to output anisomerization unit product stream 132. The isomerization unit 130 mayproduce equilibrium xylene ratios of approximately about 50% by weightmeta-xylene, about 26% by weight ortho-xylene, and about 24% by weightpara-xylene. In other embodiments, the equilibrium xylene ratio ofpara-xylene may be under 24%, and the ratios for meta-xylene andortho-xylene would be proportionally higher. The isomerization unit 130may also crack certain hydrocarbons to form lighter molecules,categorized as fuel gas, as well as certain aromatics. The isomerizationunit 130 may be any type of isomerization unit known in the art,including, for example, a unit comprising a catalyst for adequate xyleneconversion.

Positioned downstream of the isomerization unit 130 within the xylenerecovery loop 101, the deheptanizer unit 140 may be in direct fluidcommunication with one or more of the para-xylene recovery unit 120, themembrane unit 160C, the isomerization unit 130, and the clay treater 150such that it is configured to receive, directly or indirectly, thepara-xylene lean stream 122 (e.g., from the para-xylene recovery unit120), the membrane unit product stream 162C (e.g., from membrane unit160C), or the isomerization unit product stream 132 (e.g., from theisomerization unit 130) and to output a xylene rich stream 142, a fuelgas stream 144, and a hydrocarbon stream 146 that may include C6aromatic compounds, C7 aromatic compounds, and non-aromatic compounds.The deheptanizer unit 140 may be any type of deheptanizer known in theart, including, for example, a trayed distillation column.

Positioned downstream of the deheptanizer unit within the xylenerecovery loop 101, the clay treater 150 may be in direct fluidcommunication with one or more of the deheptanizer unit 140 and thexylene splitter 110 such that it is configured to receive, directly orindirectly, the xylene rich stream 142 (e.g., from the deheptanizer unit140) and to output a clay treated stream 152, which may be fed back intothe xylene splitter 110. The clay treater 150, which may be any type ofclay treater known in the art, may be used for reacting olefin moleculesin the xylene rich stream 142.

One or more membrane units 160A, 160B, 160C, 160D may be positionedwithin the system 100 as shown in FIG. 1, and the position of themembrane unit(s) 160A, 160B, 160C, 160D within the system 100 affectsthe functions of the membrane unit(s) 160A, 160B, 160C, 160D and othercomponents within the system 100 as described in more detail for eachembodiment below. Regardless of its position within the system 100, themembrane unit(s) 160A, 160B, 160C, 160D may each be configured toreceive and generate process streams (e.g., via one or more inlet portsand one or more outlet ports). The membrane unit(s) 160A, 160B, 160C,160D may each be further configured to receive a process stream at aninlet pressure of between about 300-1500 psig using a pump the processstream containing between about 1-25% non-aromatics, mixed xylenes, C6aromatic compounds, and C7 aromatic compounds. In some embodiments, theinlet pressure may be constant and approximately between 200 to 2000psig. In other embodiments, the inlet pressure may be constant andapproximately 800 psig. In further embodiments, the process stream maycontain approximately 16.5% non-aromatics, mixed xylenes, C6 aromaticcompounds, and C7 aromatic compounds, though this percentage may vary.Functionally, the membrane unit(s) 160A, 160B, 160C, 160D may each havea xylene permeance of between 5-150 gm/m²/hr/psi (e.g., betweenapproximately 40-80 gm/m²/hr/psi in some embodiments and approximately60 gm/m²/hr/psi in other embodiments) and a xylene to non-aromaticpermeance ratio of 3-70 (e.g., between about 10-25 in some embodimentsand about 15 in other embodiments). It is advantageous to maximize boththe xylene permeance and xylene to non-aromatic permeance ratio toimprove performance, though doing so requires balancing the two valuesas the xylene permeance and xylene to non-aromatic permeance ratio areinverse to one another (e.g., increasing the value of one decreases theother) and makes the membrane unit more difficult to construct.Increasing the xylene permeance reduces the membrane surface arearequired. Increasing the xylene to non-aromatic permeance ratio providescleaner separation between xylenes and non-aromatics (e.g., at a ratioof 15, xylene is permeating through the membrane 15 times faster thannon-aromatics). The inputs, outputs, and efficiency of the membrane unitvary based on its position within the xylene recovery loop.

Structurally, membrane unit(s) 160A, 160B, 160C, 160D may each include aone-stage or multi-stage (e.g., two-stage) membrane system. A one-stagesystem may be configured to remove approximately 50% of non-aromaticspresent in an inlet stream while losing approximately 10% of aromaticspresent in the inlet stream, the aromatics comprising mixed xylenes. Atwo-stage or other multi-stage membrane system may remove approximately50% of non-aromatics present in an inlet stream while reducing the lossof aromatics to half of that of single stage membrane system. Addingstages to the membrane unit(s) increases purity of the xylenes that itpreferably permeates, though it costs more to construct and maintain.

The structure and materials of the membrane(s) making up the membraneunit(s) 160A, 160B, 160C, 160D may vary. Similarly, like the structureand materials of the membrane(s), the position of the membrane unit(s)160A, 160B, 160C, 160D within the xylene recovery loop 101 may impactits performance and overall performance of the system 100.Functionalities of the membrane unit(s) 160A, 160B, 160C, 160D at theirrespective positions are described in more detail below.

Membrane Unit 160A

In one embodiment of system 100, the membrane unit 160A may bepositioned upstream of the xylene splitter 110 such that it isconfigured to receive the reformate stock stream 102 (e.g., from asource external to the system 100) and in direct fluid communicationwith the xylene splitter 110. The reformate stock stream 102 may includenon-aromatic compounds, mixed xylenes, C6 aromatic compounds, and C7aromatic compounds. In this position, the membrane unit 160A may befurther configured to produce the membrane unit product stream 162A andthe non-aromatics rich stream 164A.

In this configuration of the system 100, the xylene splitter 110 may bein direct fluid communication with the membrane unit 160A and configuredto receive (e.g., via one or more inlet ports) the membrane unit productstream 162A and produce and expel (e.g., via one or more outlet ports)the mixed xylene stream 112 and the heavier hydrocarbon stream 114 thatmay include C9 and C10 hydrocarbons.

The para-xylene recovery unit 120 may be in direct fluid communicationwith the xylene splitter 110 and configured to receive the mixed xylenestream 112 and produce the para-xylene lean stream 122 and thepara-xylene rich stream 124. The para-xylene recovery unit 120 may beconfigured to direct the para-xylene rich stream 124 out of the system100 as a product and direct the para-xylene lean stream 122, whichincludes mixed xylenes, downstream within the system 100 for furtherprocessing.

The isomerization unit 130 may be in direct fluid communication with thepara-xylene recovery unit 120 and the deheptanizer unit 140 such that itis configured to receive the para-xylene lean stream 122 from thepara-xylene recovery unit 120 and the hydrogen stream 104 from ahydrogen source (not shown) outside of the system 100 and produce theisomerization unit product stream 132. The isomerization unit 130 may beconfigured to direct the isomerization unit product stream 132 to thedeheptanizer unit 140.

The deheptanizer unit 140 may be in direct fluid communication with theisomerization unit 130 and the clay treater 150 such that it isconfigured to receive the isomerization unit product stream 132 from theisomerization unit 130 and produce the xylene rich stream 142, the fuelgas stream 144, and the hydrocarbon stream 146. The hydrocarbon stream146 may include C6 aromatic compounds, C7 aromatic compounds, andnon-aromatic compounds. The deheptanizer unit 140 may be configured todirect the xylene rich stream 142 to the clay treater 150 and direct thefuel gas stream 144 and the hydrocarbon stream 146 outside of the system100.

The clay treater 150 may be in direct fluid communication with thedeheptanizer unit 140 and the xylene splitter 110 such that it isconfigured to receive the xylene rich stream 142 from the deheptanizerunit 140 and produce the clay treated stream 152, which may be fed backinto the xylene splitter 110.

Membrane Unit 160B

In one embodiment of system 100, the membrane unit 160B may bepositioned between the xylene splitter 110 and the para-xylene recoveryunit 120 such that it is configured to receive the mixed xylene stream112 (e.g., from the xylene splitter 110) and in direct fluidcommunication with the xylene splitter 110. In this position, themembrane unit 160B may be further configured to produce the membraneunit product stream 162B and the non-aromatics rich stream 164B.

In this configuration of the system 100, the xylene splitter 110 may bein direct fluid communication with the membrane unit 160B and configuredto receive (e.g., via one or more inlet ports) the reformate stockstream 102 and produce and expel (e.g., via one or more outlet ports)the mixed xylene stream 112 and the heavier hydrocarbon stream 114 thatmay include C9 and C10 hydrocarbons.

The para-xylene recovery unit 120 may be in direct fluid communicationwith the membrane unit 160B and configured to receive the membrane unitproduct stream 162B and produce the para-xylene lean stream 122 and thepara-xylene rich stream 124. The para-xylene recovery unit 120 may beconfigured to direct the para-xylene rich stream 124 out of the system100 as a product and direct the para-xylene lean stream 122, whichincludes mixed xylenes, downstream within the system 100 for furtherprocessing.

The isomerization unit 130, the deheptanizer unit 140, and the claytreater 150 may be configured to operate in the same or similar fashionas previously described in the embodiment of membrane unit 160A.

Membrane Unit 160C

In one embodiment of system 100, the membrane unit 160C may bepositioned between the para-xylene recovery unit 120 and theisomerization unit 130 such that it is configured to receive thepara-xylene lean stream 122 (e.g., from the para-xylene recovery unit120) and in direct fluid communication with the para-xylene recoveryunit 120. In this position, the membrane unit 160C may be furtherconfigured to produce the membrane unit product stream 162C and thenon-aromatics rich stream 164C.

In this configuration of the system 100, the xylene splitter 110 may bein direct fluid communication with the para-xylene recovery unit 120 andconfigured to receive (e.g., via one or more inlet ports) the reformatestock stream 102 and produce and expel (e.g., via one or more outletports) the mixed xylene stream 112 and the heavier hydrocarbon stream114 that may include C9 and C10 hydrocarbons.

The para-xylene recovery unit 120 may be in direct fluid communicationwith the xylene splitter 110 and configured to receive the mixed xylenestream 112 and produce a para-xylene lean stream 122 and a para-xylenerich stream 124. The para-xylene recovery unit 120 may be configured todirect the para-xylene rich stream 124 out of the system 100 as aproduct and direct the para-xylene lean stream 122, which includes mixedxylenes, downstream within the system 100 for further processing.

The isomerization unit 130 may be in direct fluid communication with themembrane unit 160C such that it is configured to receive the membraneunit product stream 162C and the hydrogen stream 104 from a hydrogensource (not shown) outside of the system 100 and produce theisomerization unit product stream 132. The isomerization unit 130 may beconfigured to direct the isomerization unit product stream 132 to thedeheptanizer unit 140.

The deheptanizer unit 140 and the clay treater 150 may be configured tooperate in the same or similar fashion as previously described in theembodiment of membrane unit 160A.

Membrane Unit 160D

In one embodiment of system 100, the membrane unit 160D may bepositioned downstream of the deheptanizer unit 140 such that it isconfigured to receive the hydrocarbon stream 146 (e.g., from thedeheptanizer unit 140) and in direct fluid communication with thedeheptanizer unit 140. In this position, the membrane unit 160D may befurther configured to produce the membrane unit product stream 162D andthe non-aromatics rich stream 164D.

In this configuration of the system 100, the xylene splitter 110 may beconfigured to operate in the same or similar fashion as previouslydescribed in the embodiment of membrane unit 160C.

The para-xylene recovery unit 120 and the isomerization unit 130 may beconfigured to operate in the same or similar fashion as previouslydescribed in the embodiment of membrane unit 160A.

The deheptanizer unit 140 may be in direct fluid communication with theisomerization unit 130, the membrane unit 160D, and the clay treater 150such that it is configured to receive the isomerization unit productstream 132 from the isomerization unit 130 and produce the xylene richstream 142, the fuel gas stream 144, and the hydrocarbon stream 146. Thehydrocarbon stream 146 may include C6 aromatic compounds, C7 aromaticcompounds, and non-aromatic compounds. The deheptanizer unit 140 may beconfigured to direct the xylene rich stream 142 to the clay treater 150,the fuel gas stream 144 outside of the system 100, and the hydrocarbonstream 146 to the membrane unit 160D.

The clay treater 150 may be configured to operate in the same or similarfashion as previously described in the embodiment of membrane unit 160A.

Described below are example methods for removing non-aromatic compoundsfrom a xylene isomerization process for para-xylene production inaccordance with example embodiments. These methods may be used inconjunction with the system of FIG. 1 in multiple configurations.

FIG. 2 illustrates a method 200 for removing non-aromatic compounds froma xylene isomerization process for para-xylene production with themembrane unit 160A in the first position. As shown in FIG. 2, the method200 may commence at operation 202 with feeding the reformate stockstream 102 through the membrane unit 160A, which may be configured toproduce the membrane unit product stream 162A and the non-aromatics richstream 164A. At operation 204, 160A may feed the membrane unit productstream 162A to the xylene splitter 110, which may be configured toproduce the mixed xylene stream 112 and the heavier hydrocarbon stream114. At operation 206, the xylene splitter 110 may feed the mixed xylenestream 112 to the para-xylene recovery unit 120, which may be configuredto produce the para-xylene lean stream 122 and the para-xylene richstream 124. At operation 208, the para-xylene recovery unit 120 may feedthe para-xylene lean stream 122 to the isomerization unit 130, which maybe configured to produce the isomerization unit product stream 132. Atoperation 210, the isomerization unit 130 may feed the isomerizationunit product stream 132 to the deheptanizer unit 140, which may beconfigured to produce the xylene rich stream 142, the fuel gas stream144, and the hydrocarbon stream 146. At operation 212, the deheptanizerunit 140 may feed the xylene rich stream 142 to the clay treater 150,which may be configured to produce the clay treated stream 152. Atoperation 214, the clay treater 150 may feed the clay treated stream 152to the xylene splitter 110 for recirculation within the xylene recoverloop 101. Alternatively, the clay treated stream 152 may be outputtedfrom the system 100 rather than recirculated through the xylene recoveryloop 101. It should be noted that method 200 may be stopped at anyoperational step with the output stream(s) of that step being sold toanother processing plant.

FIG. 3 illustrates a method 300 for removing non-aromatic compounds froma xylene isomerization process for para-xylene production with themembrane unit 160B in the second position. As shown in FIG. 3, themethod 300 may commence at operation 302 with feeding the reformatestock stream 102 through the xylene splitter 110, which may beconfigured to produce the mixed xylene stream 112 and the heavierhydrocarbon stream 114. At operation 304, the xylene splitter 110 mayfeed the mixed xylene stream 112 to the membrane unit 160B, which may beconfigured to produce the membrane unit product stream 162B and thenon-aromatics rich stream 164B. At operation 306, the membrane unit 160Bmay feed the membrane unit product stream 162B to the para-xylenerecovery unit 120, which may be configured to produce the para-xylenelean stream 122 and the para-xylene rich stream 124. At this point, themethod 300 may be stopped with the output para-xylene lean stream 122and the para-xylene rich stream 124 being sold to another processingplant. Alternatively, although not shown, the method 300 may proceedwith directing one or more of those output streams for furtherprocessing to one or more of the isomerization unit 130, thedeheptanizer 140, the clay treater 150, and/or one or more additionalmembrane units 160C, 160D.

FIG. 4 illustrates a method 400 for removing non-aromatic compounds froma xylene isomerization process for para-xylene production with themembrane unit 160C in the third position. As shown in FIG. 4, the method400 may commence at operation 402 with feeding the reformate stockstream 102 to the xylene recovery loop 101 (e.g., specifically to thexylene splitter 110). In turn, at operation 404, the xylene splitter maybe configured to produce the mixed xylene stream 112 and the heavierhydrocarbon stream 114. As the mixed xylene stream 112 continuesdownstream to the para-xylene recovery unit 120, at operation 406, thepara-xylene recovery unit 120 may be configured to produce thepara-xylene lean stream 122 and the para-xylene rich stream 124. Atoperation 408, after the para-xylene recovery unit 120 has fed thepara-xylene lean stream 122 to the membrane unit 160C, the membrane unit160C may be configured to preferably permeate xylenes to separate themembrane unit product stream 162C from the non-aromatics rich stream164C. At operation 410, after the membrane unit 160C has fed themembrane unit product stream 162C to the isomerization unit 130, theisomerization unit 130 may be configured to process the membrane unitproduct stream 162C to produce the isomerization unit product stream132, which can then be fed to the deheptanizer unit 140. At operation412, the deheptanizer unit 140 may be configured to produce one or morestreams of the xylene rich stream 142, the fuel gas stream 144, and thehydrocarbon stream 146, and at least the xylene rich stream 142 may befed downstream to the clay treater 150. At operation 414, the claytreater 150 may be configured to produce the clay treated stream 152,which can then be fed through the xylene splitter 110 for recirculationwithin the xylene recovery loop 101 at operation 416. Alternatively, theclay treated stream 152 may be output from the system 100. By separatingthe non-aromatics rich stream 164C, it can be removed from the system100 without adversely impacting system efficiency or effectiveness(e.g., without having to discard streams that are more concentrated withxylenes and/or stopping operations).

FIG. 5 illustrates a method 500 for removing non-aromatic compounds froma xylene isomerization process for para-xylene production. As shown inFIG. 5, the method 500 may commence at operation 502 with feeding thereformate stock stream 102 through the xylene splitter 110, which may beconfigured to produce the mixed xylene stream 112 and the heavierhydrocarbon stream 114. At operation 504, the xylene splitter 110 mayfeed the mixed xylene stream 112 to the para-xylene recovery unit 120,which may be configured to produce the para-xylene lean stream 122 andthe para-xylene rich stream 124. At operation 506, the para-xylenerecovery unit 120 may feed the para-xylene lean stream 122 to theisomerization unit 130, which may be configured to produce theisomerization unit product stream 132. At operation 508, theisomerization unit 130 may feed the isomerization unit product stream132 to the deheptanizer unit 140, which may be configured to produce thexylene rich stream 142, the fuel gas stream 144, and the hydrocarbonstream 146. At operation 510, the deheptanizer unit 140 may feed thehydrocarbon stream 146 to the membrane unit 160D, which may beconfigured to produce the membrane unit product stream 162D and thenon-aromatics rich stream 164D. At this point, the method 500 may bestopped with the output membrane unit product stream 162D being sold toanother processing plant. Alternatively, although not shown, the method500 may proceed with directing one or more of those output streams forfurther processing to one or more of the clay treater 150 and/or one ormore additional membrane unit(s) 160D.

While the present disclosure has been described in connection with aplurality of exemplary aspects, as illustrated in the various figuresand discussed above, it is understood that other similar aspects can beused, or modifications and additions can be made, to the describedaspects for performing the same function of the present disclosurewithout deviating therefrom. For example, in various aspects of thedisclosure, methods and compositions were described according to aspectsof the presently disclosed subject matter. However, other equivalentmethods or compositions to these described aspects are also contemplatedby the teachings herein. Therefore, the present disclosure should not belimited to any single aspect, but rather construed in breadth and scopein accordance with the appended claims.

It is to be understood that the embodiments and claims disclosed hereinare not limited in their application to the details of construction andarrangement of the components set forth in the description andillustrated in the drawings. Rather, the description and the drawingsprovide examples of the embodiments envisioned. The embodiments andclaims disclosed herein are further capable of other embodiments and ofbeing practiced and carried out in various ways. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting theclaims.

Accordingly, those skilled in the art will appreciate that theconception upon which the application and claims are based may bereadily utilized as a basis for the design of other structures, methods,and systems for carrying out the several purposes of the embodiments andclaims presented in this application. It is important, therefore, thatthe claims be regarded as including such equivalent constructions.

Furthermore, the purpose of the foregoing Abstract is to enable thevarious patent offices and the public generally, and especiallyincluding the practitioners in the art who are not familiar with patentand legal terms or phraseology, to determine quickly from a cursoryinspection the nature and essence of the technical disclosure of theapplication. The Abstract is neither intended to define the claims ofthe application, nor is it intended to be limiting to the scope of theclaims in any way. Instead, it is intended that the invention is definedby the claims appended hereto.

1. A method for removing non-aromatic compounds from a para-xyleneproduction process, comprising: feeding a reformate stock stream into axylene recycle loop comprising a xylene splitter, a para-xylene recoveryunit, a membrane unit, an isomerization unit, a deheptanizer unit, and aclay treater; producing, via the xylene splitter configured to receivethe reformate stock stream, a mixed xylene stream comprisingpara-xylene, ortho-xylene, and meta-xylene; producing, via thepara-xylene recovery unit configured to receive the mixed xylene stream,a para-xylene lean stream; preferentially permeating xylene in thepara-xylene lean stream via the membrane unit to separate anon-aromatics rich stream from a membrane unit product stream;processing the membrane unit product stream in the isomerization unit toproduce an isomerization unit product stream; producing, via thedeheptanizer unit configured to receive the isomerization unit productstream, a xylene rich stream; processing the xylene rich stream throughthe clay treater to produce a clay treated stream; and feeding the claytreated stream into the xylene splitter for recirculation within thexylene recycle loop.
 2. The method of claim 1, wherein the reformatestock stream comprises non-aromatic compounds, mixed xylenes, C6aromatic compounds, and C7 aromatic compounds.
 3. The method of claim 1,wherein preferentially permeating the xylenes from the para-xylene leanstream via the membrane unit further comprises feeding the para-xylenelean stream into the membrane unit at a constant pressure between 200 to2000 psig.
 4. The method of claim 1, wherein the membrane unit comprisesa one-stage membrane system.
 5. The method of claim 1, wherein themembrane unit comprises a multi-stage membrane system.
 6. The method ofclaim 1, wherein the membrane unit presents a xylene permeance of 60gm/m²/hr/psi and a xylene to non-aromatic permeance ratio of
 15. 7. Themethod of claim 1, further comprising producing, via the deheptanizerunit, a hydrocarbon stream.
 8. The method of claim 7, wherein theisomerization unit product stream comprises 50 wt % meta-xylene, 24 wt %para-xylene, and 26 wt % ortho-xylene.
 9. The method of claim 7, whereinthe hydrocarbon stream comprises C6 aromatic compounds, C7 aromaticcompounds, and non-aromatic compounds.
 10. A non-aromatic compoundremoval system, comprising: a xylene splitter configured to receive areformate stock stream and produce a mixed xylene stream; a para-xylenerecovery unit in direct fluid communication with the xylene splitter andconfigured to receive the mixed xylene stream from the xylene splitterand produce a para-xylene lean stream; a deheptanizer unit in fluidcommunication with the para-xylene recovery unit and configured toproduce a hydrocarbon stream; and a membrane unit configured to receiveone or more streams of the para-xylene lean stream and the hydrocarbonstream and produce a non-aromatics rich stream, wherein the membraneunit presents a xylene permeance of 60 gm/m²/hr/psi and a xylene tonon-aromatic permeance ratio of
 15. 11. The system of claim 10, whereinthe deheptanizer unit is further configured to produce a xylene richstream, the system further comprising a clay treater in direct fluidcommunication with the deheptanizer unit and the xylene splitter, theclay treater being configured to receive the xylene rich stream from thedeheptanizer unit and produce a clay treated stream, and feed the claytreated stream to the xylene splitter.
 12. The system of claim 10,wherein the para-xylene lean stream is fed into the membrane unit at aconstant pressure between 200 to 2000 psig.
 13. The system of claim 10,wherein the hydrocarbon stream is fed into the membrane unit at aconstant pressure between 200 to 2000 psig.
 14. The system of claim 10,wherein the membrane unit comprises a one-stage membrane system.
 15. Thesystem of claim 10, wherein the membrane unit comprises a multi-stagemembrane system.
 16. A method for removing non-aromatic compounds from apara-xylene production process, comprising: feeding a reformate stockstream into a xylene splitter, the xylene splitter producing a mixedxylene stream, the mixed xylene stream comprising para-xylene,ortho-xylene, and meta-xylene; feeding the mixed xylene stream through amembrane unit, the membrane unit producing a non-aromatics rich streamand a membrane unit product stream; processing the membrane unit productstream in a para-xylene recovery unit, the para-xylene recovery unitproducing a para-xylene lean stream; processing the para-xylene leanstream in an isomerization unit, the isomerization unit producing anisomerization unit product stream; feeding the isomerization unitproduct stream into a deheptanizer unit, the deheptanizer unit producinga xylene rich stream; processing the xylene rich stream through a claytreater, the clay treater producing a clay treated stream; and feedingthe clay treated stream into the xylene splitter.
 17. The method ofclaim 16, wherein the mixed xylene stream is fed into the membrane unitat a constant pressure between 200 to 2000 psig.
 18. The method of claim16, wherein the membrane unit comprises a one-stage membrane system. 19.The method of claim 16, wherein the membrane unit comprises amulti-stage membrane system.
 20. The method of claim 16, wherein themembrane unit presents a xylene permeance of 60 gm/m²/hr/psi and axylene to non-aromatic permeance ratio of 15.